Apparatus for burning fuel



March 24, 1942- l R. E. BREsSLr-JR 7 2,277,630

APPARATUS FOR BURNING FUEL Filed March 16, 1959 4 Sheets-Sheet l March 24, 1942.

R. E. BRESSLER APPARATUS FOR BURNING FUEL 4 Sheets-Sheet 2 Filed March 16, 1939 March 24, 1942. R. E'. BRESSLER 2,277,630

' APPARATUS FOR BURNING FUEL Filed March 16, 1939 4 Sheets-Sheet 5 13.9 90 m 7 F284 m 93 March 24, 1942.

R. E. BRESSLER I APPARATUS FOR BURNINGVFUEL Filed March 16, 1939 4 Sheets-Sheet 4 THE 0105 74 T TIME/IMOTOI? IN TERRUPTEI? 514! TC P55551185 C 8 4 9 a 570mm MOT0 MMPEI? Norm Z 5 wzfz/ Patented Mar. 24, 1942 APPARATUS FOR BURNING FUEL Robert E. Bressler, Oregon, 111., assignor to Kol- Master Corporation, Oregon, 111., a corporation of Illinois Application March 16, 1939, Serial No. 262,194

7 Claims.

This invention relates to improvements in methods of and apparatus for burning fuel and it consists of the matters hereinafter described and more particularly pointed out in the appended claims. The apparatus embodying one phase of the invention is a stoker of the underfeed type.

In the operation of fuel burning apparatus, such as an underfeed stoker, the load demand varies to a considerable extent, both as regards the period of the day and the period of the year.

In a conventional fuel burning stoker, it is necessary that the same be set to burn fuel at a predetermined rate and that a change be made in some adjustment embodied, in the stoker, by the user, to change the burning rate to accommodate the load demand.

The volume of air delivered by the blower of the stoker, against a fixed resistance, will be constant but should the stoker remain inoperative for any appreciable period of time, the resistance to the passage of the air through the fuel bed will decrease due to burning away of the fuel during the off period. Thus long off or standby periods tend to reduce the depth of thickness of the fuel bed to a point where an excess of air will be caused to pass through the fuel bed when the apparatus starts operation. This is a condition which should be avoided for reasons that are apparent.

Heretofore, many attempts have been made to control the volume of air for proper combustion by providing a given volume thereof for a given rate of feed or to vary the volume of air with the fuel bed depth or resistance or to vary the air rate movement to increase the volume with an increase in fuel bed resistance and to decrease the volume of air with a decrease in fuel-bed resistance.

The correct depth of the fuel bed on a stoker is a function of the design of the stoker retort and should not vary materially. Controls for stokers as heretofore made have not been of sufficient sensitivity to perform the function for which they'were designed because the proper control apparatus therefor would cost more than .the market would or could pay. In burning a coking or caking coal, it is especially desirable that such coal be fed at a rate either faster or slower than the burning rate of the fuel bed in order to break up the coking or caking effect produced in burning such fuels.

The reason a stoker of the ordinary type functions at all is that the inefiiciency of combustion will finally reach a balance with the inefficiency of the distribution of fuel and air so that the fuel bed will remain at a predetermined depth even though sufficient air is being supplied to burn many times the fuel being fed. However, with such an inefiicient action, much of the air will pass up the stack, and will actually remove heat from the burning fuel bed instead of being utilized in the combustion process.

One of the objects of the present invention is to provide an apparatus for burning fuel which overcomes the objections hereinbefore mentioned and which apparatus may be set at the factory so that the user will not be required to make adjustments and yet the apparatus will function efficiently under varying load conditions or demands.

Another object of the invention is to provide an improved method of burning fuel, involving a new principle in the supplying of air to the fuel bed to control the burning rate of the bed with respect to the fuel feeding rate, in one instance to have a burning rate which is lower than the fuel feeding rate and in another instance to have a burning rate which is higher than the fuel feeding rate.

'A further object of the invention is to provide an apparatas in the nature of a stoker wherein the fuel is fed into the retort in a manner pro- Viding a better lifting action at the end of the feed screw and wherein the fuel is also prevented from packing against the end of the screw.

Again it is an object of the invention to provide a novel means for providing a more uniform feed of fuel from the hopper into the feed screw duct or tube and which is relatively constant regardless of the amount of fuel in the hopper and regardless of the kind or size of the coal therein.

Also, it is an object of the invention to provide a stoker structure which though automatic and eflicient in operation, is simple in construction for low cost production and which requires no attention by the user other than to keep an adequate supply of coal in the hopper and remove tus as taken on the line 3-3 of Fig. l, a part of the hopper appearing as broken away better to show parts beneath the same.

Fig. 4 is a transverse detail vertical sectional view on the scale of Fig. 3, through the retort end of the apparatus, the plane of the section being indicated by the line 4-4 of Fig. 1.

Fig. 5 is a longitudinal vertical section view through the retort end of the apparatus as taken on the line 5-5 of Fig. 4.

Fig. 6 is a detail longitudinal vertical sectional view through the front end portion of the apparatus as taken on the line 5-6 of Fig. 3.

Fig. 7 is a detail transverse vertical sectional view through the front end portion of the apparatus as taken on the line 'l'l of Fig. 3.

Fig. 8 is a detail transverse vertical sectional view on an enlarged scale through that portion of the air duct containing the control damper, the plane of the section being taken on the line 8--8 of Fig. 3.

Fig. 9 is a view in side elevation of the parts appearing in Fig. 8. a

Fig. 10 is a view in side elevation of the casing of the blower embodied in the apparatus and which will be more fully referred to later.

Fig. 11 is a diagrammatic view of the control circuit for the apparatus and which will also be more fully referred to later.

Fig. 12 is a transverse vertical detail sectional view through a part of the apparatus as taken on the line l2-l2 of Fig. 3.

Referring now in' detail to that embodiment of the invention illustrated in the drawings, the improved fuel burning apparatus which is in the form of an underfeed stoker, includes as best shown in Fig. 1 a burner l5, a hopper I6, and a means I! whereby fuel is fed from the hopper to the burner. Said apparatus also includes a blower l8 for supplying the necessary air under pressure, a duct IQ for conveying the air under pressure to the burner and a motor 20 which in this instance drives both the fuel feeding means and the blower.

The burner l5 comprises a hollow windbox 2| in which a retort 22 is located in suitable relation to provide a chamber in said windbox surrounding the retort, saidwindbox having an air inlet 2| a in its front bottom end. At the'top of the windbox is a dead plate 23 and arranged between the inner margin of the dead plate and the top of the retort are the tuyres 24 whereby air under pressure is admitted from the windbox chamber to the fuel bed for combustion purposes. The retort transversely considered is of a V-shaped cross section as appears in Fig. 4 and is formed with a rounded bottom 25. The rear end 26 of the bottom portion of the retort is perpendicular while the rear end 21 of the top portion thereof, is flared upwardly and rearwardly as best appears in Fig. 5. The front end of the bottom portion of the retort is formed with a fuel inlet opening 28, above which a portion 29 of the retort slopes upwardly and rearwardly to join the vertical front end 30 of the top portion of the retort.

The fuel feeding means I! before mentioned includes a feed tube section 3| between the rear end of the lower portion of the hopper IS and the fuel inlet opening 28 of th burner and a second tube section 32. The last mentioned section is in axial alignment with the first mentioned one and is arranged between the front end of the lower portion of the hopper I8 and the rear side of an upright casing 33 located in front of the hopper. In the tube sections 3l-32, which are disposed in the longitudinal median line of the hopper I5, is located a feed screw 34 which includes a shaft 35 and a flight 36 thereon of a diameter approximating that of the inside diameter of the said tube sections 3l--32.

The feed screw 34 extends from casing 33 through the tube section 32, the bottom of the hopper I6 and through the tube section 31 into the rounded bottom portion 25 of the retort. The last half turn of the flight 36 terminates short of the end of the shaft and in advance of the vertical plane of the front top wall portion of the retort. The rear end of the shaft has no bearing in the vertical wall portion 26 of the retort but it is provided with a feeding disk 31 arranged closely adjacent said wall, the disk having a diameter approximating that of the flight 36.

With the feed screw and retortconstruction made as described, certain advantages are obtained. As the fuel (usually coal) enters the inlet 28 of the retort, the extremity of the flight in a part of its rotation exerts a lifting action on the fuel.

In another portion of its rotation, it packs the fuel against the disk section 31 which, with continued rotation, exerts a lifting action thereon. Therefore, the extremity of the screw and the disk coact in producing an upward lifting action substantially in the central portion of the retort which causes the fuel at the top of the re tort to feed outwardly from th center so as to be distributed evenly to all parts of the fuel bed on the retort. With the construction described, no bearing trouble is encountered for the rear end of the shaft of the screw because the disk forms its own bearing in the'fuel at the rear of the bottom portion of the retort and tends to rest on the bottom of the retort reacting against the lifting action on the fuel.

That part of the feed screw 34 .between the tube sections 3l-32 is disposed just above the bottom I60. of the hopper (see Fig. 12) and which bottom is flat and horizontally disposed. At the bottom of the hopper and arranged one on each side of,.. that portion of the feed screw in the hopper are feeding disks 48 and 4| respectively, each journalled on an upstanding stud 42 rising from the bottom of the hopper. Each feeding disk or Wheel has a top wall 43 arranged in the horizontal plane of the shaft 35 of the feed screw, and 2. depending marginal flange 44 which extends approximately to the bottom of the hopper. as best appears in Fig. 12. The flange 44 prevents tilting of the associated feeding disk. On the periphery of both disks are teeth 45 which engage with the advancing face of the flight of the feed screw 34. This engagement while driving the feeding disks in opposite directions, makes the peripheral portions of both disks, associated with the screw. feed fuel toward the inlet end of the feed tube section 3| and with continued movement, move excess fuel away from the inlet to prevent packing of fuel at that point.

A relatively large worm gear 46 is fixed to that end of the shaft 35 of the screw 34 arranged in the casing 33 and in the top end of said casing is journalled a transverse shaft 41. This shaft carries a worm 48 which meshes with the worm gear 46 fixed to the feed screw shaft as before described. The right hand end of the shaft 41 as appears in Fig. 2 extends outwardly beyond the associated side of the casing and there has fixed to it a plurality or a set of stepped pulleys of stepped pulleys 51--58 and 59 respectively fixed thereon which successively decrease in diameter outwardly from the associated end of the motor. The pulleys in one set are arranged in the'planes of the pulleys of the other set and a belt 60 is provided to drive one pulley in one set from an associated one in another set. By changing the belt from one pair ofassociated pulleys in both sets thereof to another pair of associated pulleys thereof, it is possible to provide a number of different speed ratios of the drive between the motor 20 and the shaft 41. It is of course apparent that this change of speed ratios betweenthe motor 20 and the shaft 41 may be obtained through other means than the sets of pulleys and associated belt and the latter is illustrated and described as substantially the simplest arrangement by which this change in speed ratios may be obtained.

The left hand end of the armature shaft extends into the blower casing I8 where it has fixed to it a rotor or fan of any desired type but not shown herein. The left hand side of the blower casing, which is of the bottom discharge type is provided with an air inlet opening 20a and associated therewith is a pivoted inlet damper 6| (see Fig. 10) whereby the volume of air admitted into the blower casing may be controlled. Said damper carries an indicator or pointer 62 which cooperates with numerals 63 on the associated side of the casing. These numerals accord with the setting of the belt 60 with respect to associated pulleys in the sets49-58 and and 51-58 and 59 respectively. Thus, the volume of air admitted to the blower may be coordinated with the ratio at which the screw 34 feeds fuel to the retort 22.

An air duct 65 connects the discharge side of the blower l8 with the inlet 2la of the windbox and this duct is arranged in a plane below that of the hopper l6 so as to pass beneath the-same. .In said duct which is of a rectangular cross section, is located a control damper 66 whereby the volume of air delivered by the blower to the retort is controlled independently of the volume inlet control damper 6| of the blower. The

damper 66 is mounted on a horizontal shaft 61 journalled at its ends in the opposed side walls of the duct 65 as best appears in Figs. 8 and 9. One end of said shaft projects beyond the outer side wall of the duct 56 and has an actuating member 68 in the forin of a pulley fixed thereto. A weight 69 is fixed to the outer face of the pulley, which by gravity tends to turn the damper 66 to its closedposition as limited by a stop 10 carried on the inner face of the pulley when the same engages the underside of the duct. When the damper is in substantially closed position wherein it stands in a vertical plane, suflicient air may pass about its edges to support comfor the passage of that volume of air which will support combustion of the fuel bed at the maximum burning rate.

An upright bracket II is fixed to the top of the duct 65 above the damper. and this bracket supports a small electric torque motor 12 on that side facing the pulley. This torque motor is of the kind which may be stalled, when energized without harm. It includes a rotatable shaft 13 which, overhangs the pulley 68 and a belt 14 is trained about said pulley and the overhanging end of the shaft 13.

When the motor I2 is energized, it drives the pulley 68 clockwise, as viewed in Fig. 9, to turn the damper from its substantially closed vertical position to substantially wide open horizontal position. Thus the damper turns through an angle of at which time the stud 18 again engages the bottom of the duct so that the weight 69 is in the dot and dash line position of Fig. 9. At this time, the motor 12 is stalled. When'the motor is deenergized, the weight 69 operates to turn the wheel 68 counterclockwise to close the damper 66.

On the top side of the shelf 52 is located a control or a pressure switch indicated as a'wholeoppositely facing casing parts 16 and TI respectively,.each having an outwardly extending radial marginal flange. A flexible diaphragm 78 is clamped at its peripheral margin between the marginal flanges of the casing parts 16 and Tl. Rigid disks 79 are secured to opposite sides of the diaphragm 18 by means of an axially disposed upwardly extending stem 80 and associated nuts. The stem 80 passes through an axial hole in the top casing part 15, and an expansion spring 8! surrounds that part of the stem above the casing part and abuts at one end against said casing part and, at its other end, abuts against a nut and washer assembly 82 adjacent the top end of the stem.

The numeral 83 indicates a bearing ,bracket rising from the top of the casing part 16 near the stem 80. A lever 84 made'of insulation is pivoted to the top end of the bracket 83 by a pin 85. The lever 84 (see Fig. 7) includes two arms 86-81 extending in opposite directions. The arm 81 carries a metal thrust receiving button 83 on its underside against which the top extermity of the stem 88 normally engages. A spring contact arm 89 is so fixed to the arm 81 by a terminal 98 as to form an extension for said arm. The contact arm 89 carries an upwardly facing contact 9-I- at its outer end which is normally disengaged from a fixed contact 92 but under certain pressure conditions in the duct 65 and windbox 2| is engaged with said fixed contact. The contact 92 is carried by a'bracket 93 mounted upon a block of insulation 64 on the top of the casing part 16. Between. the bracket 93 and the end of the lever arm 81 a second bracket 95 is mounted on the insulation block and this bracket supports a permanent magnet 96 arranged above and overhanging a part of the arm 89 and the purpose of which will appear later.

The arm 86 carries an adjustable stem 9'! which engages one end of an expansion spring 98, the other end of which engages the bracket 83. As the springs 98 and 8| are located upon opposite sides of the pin 85, it is apparent they oppose each other in their action upon the arms 86 and 81 of the lever 84. Under normal conditions the spring 98 depresses the arm 81 against the action of the spring 9I so that the contact 9I is separated from the contact 92. The amount of rocking movement of the lever 84 in both directions is limited by a post 99 rising from the top casin part and extending through an opening I99 in the lever arm 86.

The post 99 is in the form of a bolt threaded into the casing part I6 and locked in place by a nut II. The post has a head I92 at its top end which limits the upward movement of the lever arm 86 and a pair of lock nuts I93 on said bolt or post limits the downward movement of said lever arm. The switch structure just above described isenclosed by a cover I94 secured to the casing part I6. The bottom chamber of the casing I as afforded by the bottom casing part II and the diaphragm I8 is connected by a tube a (see Fig. 1) with the air duct 65 at a point in advance of the damper 66, whereby, in conjunction with the spring 98, the diaphragm is actuated in either direction in accordance with changes in the pressure in said chamber.

The hopper I6 in this instance, which is made relatively low for ease in filling, is made relatively wide for capacity. It is" provided at the top with a hinged cover I95 and a part of the front portion of the hopper is made as an inwardly and downwardly extending wall I6b which better directs fuel at the front of the hopper into the operative zone of the two feeding disks 49 and M. By reason of the wall I6b, the front end portion of the hopper provides a better overhang with respect to portions of the apparatus forwardly thereof so that space is saved and a more compact arrangement of parts is'possible. To support the hopper in its desired position with respect to the floor line, it is mounted upon a base I96 and for the same reason the burner I5v is provided with feet I9I.

In Fig. 11 is illustrated one form of control circuit for the apparatus heretofore described and which circuit includes a temperature responsive device I98 in the nature of a room thermostat, a limit control I99, a transformer II9, a relay coil III and associated armature I I2 and a time controlled periodically opening and closing switch '3 respectively.

The thermostat I98 is usually located in the room or space being heated and the limit control I99, which is associated with the furnace, normally functions as a closed switch.

The transformer includes the primary and secondary windings H4 and H5. The time controlled switch includes two pairs of fixed and movable contacts, arms II6-III and II8II9 respectively and a constantly rotating shaft I29 driven in this instance by a small motor I2I. Fixed to said shaft are control disks I22 and I23 respectively, arranged in the planes of and below the con act arms Ill and H9 respectively. The contact II9 carries a tooth II9a on its under side, the purpose of which will later appear. The disk I22 has two opposed cam projections I22a on its periphery while the disk I23 has two opposed recesses I23a in its periphery. For the purpose of illustration, as to time, the shaft I29 makes one revolution per hour. The contacts H6 and H1 are normally engaged but are separated periodically for a short period of time by The contacts H8 and I I9 are normally engage periodically and remain engaged for a short period of time.

I24 and I25 indicate the main current conductors leading from a suitable source of electric current supply. The conductor- I24 leads into one side of the limit control and a line I26 leads out of the other side of said control to a contact I21 and with which the armature H2 is associated. A line I28 connects the armature II2 to one side of the main driving motor 29 and the conductor I25 is connected to the other side of.

the motor. When the armature H2 is engaged with the contact I2I, the motor 29 is energized, assuming of course that the limit control I99 is functioning as a closed switch within its operative range. When the armature I I2 is out of engagement with the contact I2'I, the motor 29 is deenergized.

The opposite ends of primary winding II4 of the transformer II9 are normally connected by lines I29 and I39 to the lines I26 and I25 respectively. One end of the secondary winding of the transformer is connected to the contact arm I I9 and to one side of the thermostat I98 by a line I3I and the other side of said secondary winding is connected by a line I32 to one side of the coil of the relay III. The other side of the thermostat is connected by a line I34 to the contact arm III. Both contacts H6 and H8 are connected by a line I35 with the other side of the relay coil III. 7

The motor I2I is connected by lines I36 and I3! to the lines I26 and I25 and therefore runs constantly so long as the limit control functions as a closed switch. The contact 92 is connected by a line I38 with the line I28 while the finger 89 is connected by a line I39 to one side of the motor 72, the other side of which is connected by a line I49 with the line I25. 9

Assume now that after a standby period, the thermostat I98 calls for heat and the contacts H6 and II! are in their closed position. Under such conditions, the pressure in the duct 65 in advance of the damper 66 is low so that the pressure in the bottom chamber of the casing I5 is likewise low. Thus the spring 98 is functioning through the lever 84 and against the spring 9| to hold the contacts 9I and 92 separated.

.When the contacts 9I--92 are separated, the

motor I2 is deenergized so that the weight 69 on the wheel 68, by gravity functions to turn the wheel orpulley 68 into a position wherein the damper 66 stands in substantially vertical position. Therefore, only the minimum volume of air may pass the same when the blower is being driven in the initial part of a fuel feeding operation as controlled by the thermostat.

. When the thermostat I98 is calling for heat, a circuit is closed through the transformer secondary winding I I 5, through the line I3 I, thermostat I98, line I34, contacts II'III6 to the line I35, through the coil of the relay I I I out through the line I 32 back to said winding. This energizes the coil of the relay III to attract its armature H2 and close the same into engagement with the contact I2I. -Thus an energizing or operating circuit is established for the motor 29 from the line I24. limit control I99, line I26, contact I 21, armature, I I2, line I28 through the motor 29 to the conductor I25.

The motor is therefore energized and operates to drive the blower I8 and at the same time drive the shaft 41 through the belt 69 and associated sets of stepped pulleys before mentioned. The drive is transmitted to the feed screw 34 through the worm 48 and the worm gear 46. of the engagement of the teeth of the disks 40-4I the latter are driven to feed fuel toward the inlet end of the feed tube section 3| which delivers it into the open front end of the retort 22. As the fuel enters the retort, the extremity of the flight 35 coacts with the disk 31 in imparting an upward lift or feed to the fuel, centrally of the top of the retort, as before described.

The rate of feeding of the fuel is much higher or greater than the rate of combustion because of the limited volume of air to support combustion which can pass the damper 85 when the same is in substantially closed position. As the feeding rate is very much higher than the low burning rate (say about on the ratio of 5 or 6 to 1) the fuel bed will rapidly build up in depth in the retort.

As the fuel bed is built up in depth, it is apparent that it increases its resistance to the passage of the small volume of air being delivered there'to so that the pressure of said air builds up in the duct. As the duct 65 is operatively connected to the bottom chamber of the diaphragm casing, it is apparent that this increase in pressure will be felt in said chamber, to flex the diaphragm I8 and move the members I9 and associated stem 88 upwardly. The stem 80 then imparts a lifting action to the arm 81 of the lever to swing it upwardly about the pin 85 as an axis but this movement ,of the lever arm is resisted by the action of the spring 98 against the other arm 86 of the lever. However, when the pressure in said bottom chamber of the diaphragm casing is such as to overcome the resistanceof the spring 98, said spring is compressed and the arm 81 swings upwardly to engage the contact 9I with the contact 92, a snap action being obtained through operation of the magnet 96.

When the contacts 9| and 92 are engaged, current flows from the line I28, through the line I38, contacts 92-9I to spring arm 89, line I39 to one side of the motor I2 and out the other side thereof through line I48 to line I25. This closes the circuit for the motor I2 to energize the same so as to function through the belt I4 and pulley 68 to swing the damper 68 into its wideopen horizontal position.

When the damper I56 is wide open, a-volume of air is delivered to the retort substantially in excess of that required to burn the amount of fuel fed by the screw to the retort so that the burning rate is higher than. the feeding rate. Thus the fuel bed is reduced in depth because at this time the burning rate is higher than the fuel feeding rate. With the fuel bed reduced in depth, the resistance to the passage of air therethrough is reduced with a corresponding pressure drop which is felt in the bottom chamber of the casing I5. The spring 98 then tends to rock the lever 84 clockwise against the resistance of the spring 8| and the magnetic pull of the magnet 96 on the arm 89, which function to hold the contact 9| engaged with the contact 92. When the pressure in said chamber of the casing I5 is such that the spring 98 overcomes the action of the spring BI and the pull of the magnet 95, the contact 9I disengages from the contact 92. This breaks the circuit for the motor I2 which becomes deenergized so that the weight 69 on the wheel 68 turns the wheel counterclockwise as viewed in Fig. 9 to return the damper to its vertical closed position.

This reduces the volume of the air fed to the fuel bed to the minimum so that the burmng By reason rate is again lower or less than the feeding rate of the fuel.

When the thermostat I08 is calling for heat so that the apparatus is functioning as before described, periodically (say once every half-hour) one of the cam projections I22a on the disk I22 will engage the contact III and lift it to break its engagement with the contact IIB. This momentarily breaks the holding circuit for the coil of the relay III so that it becomes deenergized and its armature II2 drops out of engagement with the contact I2I so that the circuit to both motors and I2 is opened. Thus both the feed screw and the blower stop and the damper 66 returns to closed position, should it have been its open positiondue to the engagement of the contacts 9I92.

of the small amount of air fed thereto and which small amount of air is that which passes the closed damped under atmospheric pressure.

With an atmospheric pressure condition existing in the duct 65, a like pressure exists in the casing I5 beneath the diaphragm I8 so that the spring 98 tends to rock the lever 84 clockwise as viewed in Fig. '7

So soon as the cam projections I22 clears the contact II I it again engages the contact H6.

If at this time the. thermostat I98 is still calling for heat, a circuit is reestablished to energize the relay coil III and this attracts the armature I I2 to engage the contact I2I to reestablish the circuit for the motor 28. With said circuit thus reestablished the feed screw 34 and the blower I8 both start operation.

Assume at this time that the fuel bed is relatively high but not at its maximum height. Thus with the damper 69 still closed and the screw feeding coal to the fuel bed, the rate of feed will be higher than the burning rate so that that fuel bed rapidly increases in depth to offer.

increased resistance to the passage of air therethrough. Therefore the air pressure builds up rapidly 'in the duct and this pressure, through the diaphragm I8 again causes engagement of the contacts 9I-82 to close the circuit to the motor I2 as before described. This opens the damper again so that a volume of air is supplied to the fuel bed which burns at a rate higher than the feeding rate.

Should the fuel bed happen to be thin, when the projection I22a clears the contact II I so that the latter again engages the contact II6, the stoker starts up as before with the damper 66 closed. The feed of fuel is again at a rate higher than the burning rate so that when the fuel bed builds up, the pressure of the air increases as before to open the damper 66 and repeat the cycle of operation. When the thermostat I98 is satisfied with heat conditions it breaks the circuit so that the motor 20 stops and the motor I2 is deenergized after which the damper 66 swings to its closed position limiting the volume of air passing through the fuel bed by reason of natural draft. I

Under light load conditions of operation when the fuel burning-apparatus is required to operate for only a short period of time, and the fuel bed is burned away during stand-by periods as much or more than is replenished during operating periods, even with the damper 66 in substantially closed position, the low burning rate During the interval that the contacts II6-I II have been separated, the fuel bed is then burning at its'lowest rate by reason mensurate with the air required for combustion of the small amount of fuel supplied, and this arrangement has the additional advantage of reducing the velocity of air passing through the furnace to one low enough so as not to carry light ash, formed during the stand-by periods, to the flues of the furnace.

With thethermostat in its off position in the rotation of the shaft I20, the tooth II9a of the contact II9 will drop into one of the recesses I23a in the disk I23 so that the contact II9 will engage the contact H8 and close the circuit to the coil I I I, which attracts its armature II 2 to engage the contact I21. This momentarily closes the circuit to the motor to start stoker operation for a short period to act as a hold fire.

By momentarily stopping the stoker during its burning operation, it is possible to automatically close the damper to produce a burning rate of the fuel bed which is lower than the feeding rate L ing the open position of the inlet damper SI for the blower. The changing of the open position of the inlet damper will notafiect the operation of the damper 66 in the duct 65 because the volume of air handled by the damper 66 when closed is so small in proportion to the volume of air passing through the inlet damper at the low burning rate that no matter what setting of damper BI is employed there will always be an adequate supply of air for operation of control I5.

Therefore, no matter what the burning rate may be, the damper 68 functions in the same way or without adjustment. The matter of different feeding rates and different positions of the damper BI is initially set at the time the apparatus is constructed. Therefore, allthat the operator must do to change the feeding and burning rate of the fuel is to change the belt 60 to the proper set of pulleys before mentioned and to set the pointer 62 of the inlet damper 6| to the proper position indicated by the corresponding numeral 63 on the blower casing.

It is pointed out that the periodic disengagement of the contacts II6-II'I as produced by the disc projections I22a, causes a corresponding periodic stoppage of the entire stoker as before described, even though the thermostat I08 still calls for heat. When the stoker stops in one of these periods, the air pressure on the diaphragm -'I8 is reduced to atmospheric pressure and the damper 56 then closes and remains closed until the motor circuit is reestablished through the reengagement of the contacts IIG-II'I. This assumes, of course, that the thermostat is still calling for heat.

When the stoker is stopped, the fuel bed burns at the low burning rate. This rate, however, is

- so low and the period is so relatively short that control switch contacts 9 I-92 are closed to again open the damper 66.

Thus, when th fuel bed is thin, the stoker operates at a low burning rate and when the fuel bed is at the correct depth, the burning rate thereof is higher than the feeding rate in order that sufiicient air be supplied. If the stoker operates to burn fuel at a rate higher than its feeding rate, the fuel bed will, of course, grow thinner. However, when the stoker is momentarily stopped, as before described, and then caused to burn at a rate lower than the feeding rate and until th fuel bed is properly rebuilt, the fuel bed can never become excessively thin and therefore, efficiency of operation of the stoker will always be high.

When the stoker starts with a thin fuel bed, the pressure in the duct I9 between the damper B6 and the fuel bed is low. The reason therefor is that only a limited volume of air can pass the damper when it is closed, and such a volume will not build up an excessive pressure because of the thin fuel bed. As the stoker continues operation, with the limited volume of air passing the closed damper, the fuel bed builds up due to insufficient air to burn the fuel as fast as it is being fed by the means II. This building up of the fuel bed continues until the air pressure in the duct I9 between the damper 66 and the fuel bed has increased to a point which will cause th diaphragm I8 to close the switch contacts 9I-92. This energizes the electrical means I2 and causes it to open the damper 65. The volume of air now passing the open damper will be sufficient to burn the fuel faster than it is being fed. When the damper opens, the air pressure in the duct between the damper 66 and. the fuel bed is much higher than when the damper is closed. Consequently the diaphragm 18 will not drop to open the contacts 9 I-92 even though the fuel bed burns away to practically, no fuel bed at all. The reason therefor is that the pressure caused by the resistance of the tuyres 24 alone, through which air must passto reach the fuel bed, when the damper is open, is greater than th pressure with the correct depth of fuel bed, with the damper 66 in its closed position.

With the construction described, so that the contacts 9I-92 will open to permit the damper 66 to close, the entire stoker is stopped periodically by. the switch I I3 to so reduce the pressure on the diaphragm as to open the contacts 9I-92 to cause deenergizing of said electrical means I2. Thereafter, because the pressure between the damper and the fuel bed has been reduced, by closing the damper 66, and if the fuel bed is thin, because of the thin fuel bed, the stoker must operate until the fuel bed is rebuilt before the damper 66 can be opened due to pressure built up between the damper and the fuel bed.

From the above, it is apparent that the structure described provides for the burning of fuel at two fixed rates, one higher than the full feeding rate of the stoker and the other one, lower than the feeding rate of the stoker and the damper I56 provides these two fixed-burning rates. In this respect, while said burning rates are mentioned as fixed, this means that said rates are fixed for any position into which inlet damper SI of the blower has been adjusted.

The term burning cycle as used in certain of the claims, means a cycle of operation of the stocker, of which there may be several, during the period th thermostat is calling for heat.

construction of the parts involved, the same isto be considered only in the illustrative sense so that I do not wish to be limited thereto except as may be specifically set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In combination with a retort, means for feeding fuel thereto to build up a fuel bed thereon, means for supplying air to the fuel bed to support combustion thereof, means responsive to the demand for heat for controlling the operation of said fuel feeding means and said air supplying means, means for controlling the volume of air supplied to the fuel bed to provide a burning rate therefor which in one instance is lower than that of the feeding rate of feul and I in another instance is higher than that of the said air supplying means.

2. In combination with a retort, means for feeding fuel thereto to build up a fuel bed thereon, air supplying means, means responsive to the demand. for heat for controlling the operation of said fuel feeding means and said air supplying I means, a duct leading from said air supplying means to said fuel bed to support combustion thereof, means in said duct for controlling the volume of air passed therethrough, means for causing said controlling means to assume a position passing but a minimum volume of air therethrough to provide a burning rate for the fuel bed which is lower than the feeding rate of fuel thereto, means operatively connected to said controlling means for causing the same to assume a position passing a maximum volume of air through the duct to provide a burning rate for the fuel bed which is higher than the feeding rate of fuel thereto, and 'means responsive to a high pressure condition of the delivered air, when said means responsive to the demand for heat is calling for heat, f0r causing said means connected to said controlling means for actuating the same to provide for the passage of a maximum volume of air to said fuel bed to provide a burning rate therefor higher than the circuit for said fuel feeding means and said air supplying means, means for controlling the volume of air supplied to the fuel bed to provide a burning rate'therefor whichin one instance is lower than the feeding rate of fuel thereto and which in another instance is higher than the feeding rat of fuel thereto and normally returning to a position providing the first mentioned burning rate, means responsive to the defuel thereto to build up the fuel bed mand for heat for controlling said electric circuit for said feeding means and said air supplying means, electrical means associated with said air volume controlling means for actuating the same to provide the maximum volume of air for the fuel bed and adapted to b connected to and disconnected from said circuit, means responsive to the pressure of air delivered to the fuel bed for connecting said electrical means to and for disconnecting it from said circuit, and means separate from said temperature responsive means operating periodically only when said temperature responsive means is calling for heat to open said circuit to stop said fuel feeding means and said air supplying means and to disconnect said electrical means from said circuit.

4. In combination with a retort, means for feeding fuel thereto to build up a fuel bed thereon. means for supplying air to said fuel bed to support the combustion thereof, means associated with said air supplying means to control the volum of air supplied to th fuel bed to one prooil ducing a burning rate for the fuel bed which is lower than the feeding rate of fuel thereto and whereby the fuel bed builds up in depth to provide that resistance to the passage of air thereto which, increases the pressure of the supplied air, and means operable through said controlling means to supply a volume of air to the fuel bed so that its burning rate is increased to one higher than the feeding rate of fuel thereto, and

means operating in a burning cycle of the stoker for periodically stopping the feeding means and said air supplying means and then restarting them to provide a burning rate for the fuel bed which is lower than the feeding rate of fuel.

5. In combination with a retort, means for feeding fuel thereto to build up a fuel bed thereon. means for supplying air to said fuel bed to support the combustion thereof, means associated with said air supplying means to control the volume'of air supplied to the fuel bed to one producing a burning rate for the fuel bed which is lower than the feeding rate of fuel thereto and whereby the fuel bed builds up in depth to provide that resistance to the passage of air thereto which i'rlcreases the pressure of the supplied air, pressure responsive means for controlling said air volume controlling means and operating under a high pressure condition of the delivered air to actuate said air volume controlling means so as to provide a volume of air for the fuel bed which increases the burning rate thereof to one higher than the feeding rate, and means operating in a burning cycle of the stoker for periodically stopping the feeding means and said air supplying means and then restarting the same to provid a low pressure condition of air to actuate the controlling means 'to provide only that volume of air which decreases the burning rate to one lower than the feeding rate.

6. In a stoker having a retort, means for automatically controlling the burning and nonburning periods of the stoker and each of which burning periods constitutes a plurality of successively occurring burning cycles, means Operating in the initial part of a burning cycle in one of the burning periods of the stoker for feeding fuel to the fuel bed on said retort, means also operating in said initial part of said cycle for 'supplying air to said fuel bed to support combustion thereof means also operating during the initial part of said cycle to control the volume of air supplied to the fuel bed so that the burning rate thereof is relatively lower than the fuel feeding rate and whereby the fuel bed increases in depth during this part of the burning cycle, means for causing said controlling means to increase the volume of air supplied to the fuel bed of increased depth in another part of said burning cycle so that the burning rate of the fuel bed becomes relatively higher than the feeding rate of fuel to said fuel bed and whereby said fuel bed is reduced in depth in this part of said burning cycle. means for stopping the feeding of fuel to the fuel bed and the supplying of air therethrough so that the fuel bed burns underv ing periods constitutes a plurality of successively occurring burning cycles, means for feeding fuel to the retort to build up a fuel bed thereon, air

supplying means, a duct leading from the air supplying means to the fuel bed to support combustion thereof, means operating to initiate a burning cycle and comprising means in said duct normally arranged to permit the passage of a minimum volume of air therethrough to the fuel bed to provide a burning rate therefor that is lower than the feeding rate of fuel thereto, said means in said duct being operable to permit the passage of a maximum volume of air to the fuel bed while feeding fuel thereto so that the burning rate of the fuel bed is higher than that of the fuel feeding rate to provide another part of said burning cycle, and means for stopping the stoker periodically during a burning period thereof and then restarting said fuel feeding means and said air supplying means to again initiate a burning cycle.

ROBERT ,E. BRESSLER. 

